Concentrically braced frames are a particularly popular choice for the lateral force resisting systems of steel structures because of their design simplicity, their low cost, the ease with which they are constructed, and the increased stiffness they provide over other lateral load resisting systems. The diagonal brace members of braced frames are subject to predominately axial forces, and in the event of a severe earthquake, seismic energy is dissipated through the cyclic yielding in tension and inelastic buckling in compression of the brace members. Typical bracing members include angles, channels, wide flange (W) sections, and rectangular and circular hollow sections.
Hollow structural sections (HSS) in particular are a common selection for lateral bracing members because of their efficiency in carrying compressive loads, their improved aesthetic appearance, and because of the wide range of section sizes that are readily available. Further, HSS have been used extensively in seismic applications to dissipate energy. Round HSS in particular have enhanced performance over rectangular HSS because of reduced residual stress concentrations.
Hollow structural sections are efficient members for carrying axial loads, however their connections are generally cumbersome, expensive, and can be difficult to design when they are used in demanding situations, including seismic applications. As well, the need for designing and constructing buildings taking into consideration seismic loads is also becoming more prevalent. Specifically, bracing is being used more often and this bracing needs to be able to withstand cyclic inelastic loading of the bracing in tension and compression.
Previously devised connectors have been focused on the residential or lightweight construction industries, providing “quick and easy” type connections not readily applicable to brace members under seismic conditions.
For example, U.S. Patent Application Publication No. 2005/0163564 to Tuell describes a construction system with interlocking connectors formed of a plate material. Although these connectors allow flexibility in assembling a structure, they may suffer undesirable connection failures during seismic loading.
Casting is a manufacturing approach that allows versatility and geometric freedom in designing a load-bearing metallic element having controlled dimensions and pre-determined performance characteristics. Because of this, the use of cast materials as structural elements is known.
For example, U.S. Pat. Nos. 6,059,482 and 6,474,902 to Beauvoir describe a bolted connector having a bulkhead for connection between a column and a beam. However, these prior art connectors are only designed to provide moment connection between a beam and column, and are not specifically designed for seismic applications. In particular, the design of these connectors does not allow for controlled yielding or developing the full strength of a bracing member.
Accordingly it would be advantageous to provide connectors for bracing members that can be mass-customized. Further it would be advantageous to provide connectors compatible with bracing members of different sizes and configurations. Still further it would be advantageous to provide connectors operable to develop the full strength of a bracing member under seismic conditions.